Frosting

That white residue on the side of your candle jar is a very common phenomenon known as "frosting". It is a natural byproduct of using natural waxes, such as soy or beeswax, and is caused by the formation of tiny, crystalline structures on the surface of the wax. 

Natural Wax Property: Soy wax is "polymorphic," meaning it forms different crystal shapes based on temperature and time. It is a sign that your candle is made of natural, non-petroleum wax.